Backup wire for fourdrinier machine



C. A. LEE

BACKUP WIRE FOR FOURDRINIER MACHINE Dec. 7, 1965 2 SheetsSheet 1 FiledDec. 14, 1961 0m Nu Dec. 7, 1965 c. A. LEE 3,222,246

BACKUP WIRE FOR FOURDRINIER MACHINE Filed Dec. 14, 1961 2 Sheets-Sheet 2United States Patent BACKUP WIRE FOR FOURDRINIER MACHINE Charles A. Lee,Knoxville, Tenn assignor to Huyck Cor poration, New York, N.Y., acorporation of New York Filed Dec. 14, 1961, Ser. No. 159,415

This present invention relates to the manufacture of felted fibrousproducts such as paper, board, pulp, asbestos-cement products and thelike, in continuous web form on machines which for convenience will bereferred to in this specification as papermaking machines. Moreparticularly, the present invention relates to the operation of the Wetend of papermaking machines of the Fourdrinier type. At the wet end ofsuch machines the fibrous web is formed from stock consisting primarilyof a suspension of fibers in water which is continuously deposited froman orifice or similar device onto a travelling endless belt ofscreen-like, material. Such screen belts may be woven from metal wire orfrom synthetic yarns, including monofilaments, multifilaments, staplefibers, or any combination thereof, and will be referred to herein atFourdrinier screens.

In papermaking machines of the type referred to above, the Fourdrinierscreen is driven through an endless path around a breast roll the uppersurface of which is located adjacent the point of deposit of the stock,a couch roll and one or more guide rolls and tensioning rolls. Theportion of the path extending from the upper surface of the breast rollto the upper surface of the couch roll is generally horizontal andconstitutes the web-forming and water extracting portions of the path.The guide rolls and tension rolls are located beneath the machine andlie in the return portion of the path which extends from the couch rollback to the breast roll.

In the web-forming portion of the path of the Fourdrinier screen thescreen passes over various devices to In the Web-forming portion of thepath of the Fourdrinier screen the screen passes over various devices tocontrol or to promote the drainage of water through the screen.Ordinarily the screen passes over forming boards adjacent the breastroll and the screen then passes over a plurality of table rolls orstationary drainage units, or combinations thereof, which cause acontrolled drainage through the screen ofa major portion of the water inthe stock, leaving the major portion of the fibers in the form of afelted web on the upper surface of the screen. The screen thenprogresses through the portion of the path in which water is extractedfrom the freshly laid web. Thus the screen usually passes over aplurality of suction boxes having flat perforated tops across which thescreen is dragged while suction is applied through the screen to extractwater from the Web of fibers carried on the upper surface of the screen.The couch roll is frequently provided with interior chambers arranged insuch a manner as to apply further suction to the web and then to releasethe suction so that the web may be continuously picked off the screen bya pick-up felt for further dewatering. The web is eventually transferredcontinuously to drying and reeling apparatus.

Formation, that is the pattern of distribution of fibers in the web, isprimarily established in the early part of the web-forming path whereabout 90% or more of the water originally in the stock rapidly drainsthrough the screen. Formation therefore is dependent upon a complexcombination of machine speed and rate of drainage of the water throughthe screen, and the partciular type of formation desired varies quitewidely between different grades of paper or other felted fibrousproducts being manufactured. For any particular product and formation itis always the desire to operate the machine at as high a rate of speedas is practicable, and in many instances the upper limit upon productionspeed is established by physical limitations imposed upon the screen asa result of the mechanical demands placed upon it. Higher speedsincrease the physical demands and thus call for stronger constructionswhich must be either coarsely woven, with large yarns or wires and largeopenings, or tightly woven with small yarns or wires and small openings.The coarse structures may afford rapid drainage but they cause markingof the screen pattern in the paper. The tightly woven structuresmay notmark the paper but the drainage rate is much slower. Theslower drainagerate means that a proportionately greater length of wire must beprovided and this compound the physical strength demands as well asincreases the cost of the screens and the paperrnaking machine.

Accordingly the design of Fourdrinier screens has requiredcorn'promisesbetween the physical demands and the desired drainage characteristicswith resultant limitation upon the speed at which paper or similarproducts may be produced with the fiber formation, uniformityof caliper,freedom from screen marking and other characteristics that may berequired.

The present invention provides supplemental screenlike belts made fromyarns of synthetic materials and preferably woven in endless form, whichare arranged to run in endless paths inside the endless paths ofFourdrinier screens. In all modifications of the present invention thesupplemental belt lies under and in direct contact with the Fourdrinierscreen in'one or more parts of the webforming and/ or the waterextracting portions of the path of the Fourdrinier screen. In oneembodiment a supplemental belt may lie beneath the Fourdrinier screen asit passes over thesuctionboxes. In otherembodiments the beltrnay remainin contact with the Fourdrinier screen as it passes around the couchroll or the breast roll or both, or substantially throughout the endlesspath thereof. These supplemental belts perform at least'one and usuallyseveral functions such as protecting the Fourdrinier screen from wear,relieving it, in varyingdegrees in different embodiments, from thestresses due to tensioning, power transmitting and supporting of thestock, as well as increasing the rate at which water may be uniformlydrained from the stock in the critical formation zone.

In one sense it is a purpose of the present invention to reduce themechanical demands placed upon Fourdrinier screens whereby the design'ofthe screens may be pointed much more sharply toward the drainage,formation or marking characteristics or combinations of thesecharacteristics required for the production of any particular product,in many cases at higher rates of speed than heretofore practical.However, the' present invention affords additional advantages which arenot directly related to the reduction of mechanical demands. Forexample, the multitudinous points of contact between the Fourdrinierscreen and the woven synthetic fabric beneath it promotes rapid anduniform drainage of water through the Fourdrinier screen irrespective ofits construction and this factor permits the use, where desired, ofFourdrinier screens of exceptionally closely-woven construction.

The present invention also affords the possibility of valuable changesin papermaking machine construction. Drastically shorter Fourdrinierscreens may be used to obtain equivalent or superior products andproduction speeds with resultant reduction in size and cost of themachine and building in which it is housed.

It also has been'discovered that the use of a durable synthetic fabricas a Fourdrinier screen coming into direct contact with thesuction'boxes or the use of such a fabric as a supplemental belt, asdisclosed herein, with a synthetic or metallic Fourdrinier screen makespossible a new combination in a paperrnaking machine of such a fabricwith suction boxes having perforated tops made of a substantiallypermanent material such as stainless steel. Since Fourdrinier screensheretofore used almost always have been made of metallic wire thesuction box tops have been made of wood or, more recently, of plastic orplastic-coated materials to reduce wear on the metal wire fabric. Thesesoft materials have wasted power because of their relatively highfrictional characteristics and have required frequent replacement orresurfacing because of irregularities, ridges and the like, worn intothem by the metallic fabric. With synthetic fabrics the wood or plasticsurfaces are not only not required but indeed are undesirable. The lifeof the synthetic fabrics may be increased several fold by using smoothmetal-surfaced perforate plates for the tops of the suction boxes andstainless steel has been found to be particularly desirable for suchuse. The amount of power required to drag the fabric over the suctionboxes is greatly reduced with the result that even greater freedom offabric design is afforded.

Other and further objects of the present invention will be understoodfrom the following description of preferred, illustrative forms of thepresent invention together with the drawings forming a part of thisspecification.

In the drawings:

FIGURE 1 is a diagrammatic side elevational view of the wet end of atypical papermaking machine embodying one form of the present invention;

FIGURE 2 is an enlarged fragmentary sectional view taken along the line2-2 in FIGURE 1;

FIGURE 3 is a view similar to FIGURE 1 showing a different embodiment ofthe present invention;

FIGURE 4 is a view similar to FIGURE 1 showing still another embodimentof the present invention;

FIGURE 5 shows a further embodiment thereof; and

FIGURE 6 is an enlarged fragmentary plan view of a portion of any of themachines shown in the preceding figures, looking down upon one of thesuction boxes with the supplemental belt, the Fourdrinier screen and thepaper mat successively broken away.

Referring now to the drawings, in FIG. 1 there is shown a Fourdrinierscreen 10 which is movable in an endless path around a breast roll 12, acouch roll 14, a return guide roll 16 of well-known construction havingedge sensing paddles 17 for automatic operation, a return roll 18 and amovable screen-tensioning roll 20. The tensioning roll 20 may be mountedin a conventional manner, for example, on an arm 22 carried on a shaft24 for angular adjustment about a horizontal axis 26. For convenience inillustration, the frame of the papermaking machine has not been shownand various supporting structures, wash rolls, showers and the like havebeen omitted.

The screen 10, in a typical machine, is driven only by the couch roll 14which is rotated by suitable means, not shown, in a clockwise directionas indicated by the arrow in FIG. 1. The remaining rolls are idlers andare rotated by the screen 10.

Above the couch roll 12 there is indicated a head box 28 having anorifice or slice 30 from which the stock 32, in the form of an aqueoussuspension of fibers flows continuously in a ribbon-like stream,frequently several inches deep, onto the screen 10 as the latter leavesthe breast roll to enter the formation zone. Illustratively there isshown a forming board 34 positioned beneath the screen 10 and extendingfrom a position closely adjacent the periphery of the breast roll 12 toa position downstream of the screen path. When a forming board or boardsare used their function is to partially impede drainage of water throughthe screen 10 for a brief period in which formation may start withgenerally horizontally disposed fibers bridging the interstices of thescreen 10.

The screen 10 progresses to a series of table rolls 36 which arerotatably supported on horizontal axes extending transversely of thepath of the screen 10. The table rolls 36, as is well known, not onlyserve to support the screen 10 with the layer of stock thereon but alsoserve to extract Water through the screen 10, separating the water fromthe fibers which are deposited in a layer upon the upper surface of thescreen 10 in desired random orientation and relatively uniformthickness. As the screen 10 passes over each table roll 36 the surfaceof the latter moves downwardly away from the screen creating a zone ofsubatmospheric pressure tending to draw water downwardly and alsotending to draw the screen itself downwardly. The diameter of the tablerolls and the speed of the screen must be carefully related to thestiffness and porosity of the screen and with the nature of the stock tominimize dipping and recovery of the screen as it passes over each tableroll. Such action frequently causes stock jump and the present inventionaffords a highly effective combination for preventing stock jump whileproviding for rapid removal of water.

In addition to the table rolls 36 there may be provided any of thewell-known forms of stationary dewatering devices. For example atransversely extending board 38 may be interposed between any or allpairs of adjacent table rolls 36 or such a board may be substituted forone or more of the table rolls. The particular form of the board 38 orequivalent stationary dewatering device or devices is not material tothe present invention. Usually these devices are adjustably mounted atthe sides of the machine so that the leading portion of the uppersurface may be brought into contact with the lower surface of theFourdrinier screen 10 and the trailing portion of the upper surface maybe inclined downwardly away from the screen to promote drainage of waterthrough the screen.

As shown in FIG. 1 the Fourdrinier screen 10 next passes over one ormore suction boxes 40 having essentially fiat tops 42 which areperforated, usually with a staggered pattern of holes or slots. Forexample, in FIG. 2 there is shown a fragment of a suction box top 42having staggered rows of holes 44 and 46 which extend transversely ofthe path of travel of the screen 10. Instead of being circular, asshown, the holes 44 and 46 may take the form of slots which may beelongated in any desired direction relative to said path of travel. Thesuction boxes 40 are connected to a suitable pump (not shown) whichexhausts the air and water from the interior of the boxes which entersthrough the screen 10 and the slots 44 and 46.

The screen 10 next progresses to the couch roll 14 which, as shown inFIG. 1, may be provided with a suction chamber 48 fixed against rotationand communicating, through a perforated rotary shell 50 of the couchroll 14 with the lower surface of the screen 10. Water is extracted fromthe stock on the screen 10 into the chamber 48 by means of a suitablepump (not shown) which continuously exhausts water and air from thechamber 48.

The structure so far described is merely illustrative of a conventioncombination of papermaking machine elements and the combination as wellas the elements may take many different forms as is well known in theart. It will be recognized that in any such combination the Fourdrinierscreen 10 must have the mechanical strength to withstand longitudinalforces due to tension and the transmission of power and to withstandbending forces at the table rolls, and it also must withstand abrasionas it comes into contact with the various rolls and stationary surfacesin its path.

In FIG. 1 the present invention is illustrated in an embodiment whichgreatly reduces frictional drag with attendant reduction in abrasivewear and in the amount of power which the screen 10 is required totransmit. In this embodiment an endless belt 52 is positioned inside theendless path of the screen 10 and is conducted through a path such thatthe belt 52 lies between the screen 10 and the tops 42 of the suctionboxes 40. The endless belt 52 is preferably wider than the screen 10 sothat the screen 10 will be supported on the belt 52 throughout its widthdurlng travel over the suction boxes, and so that the ls)c1ieen and beltmay be independently guided as described e ow.

The belt 52 may be conducted over rolls 54 and 56 located respectivelyahead of and beyond the suction boxes 40 and return rolls 58 and 60located beneath the suction boxes. One of the return rolls, for examplethe roll 60, may be a guide roll having edge sensing paddles 61 andwell-known provisions for maintaining the belt 52 centered in itsdesired path. One of the rolls 54 or 58 may be adjustable transverselyof its axis of rotation to apply such degree of tension upon the belt 52as may be desired.

It is known in the art to provide a very heavy rubber belt withperforations extending through it to run in a path approximately thesame as that just described for the belt 52. These rubber belts usuallyare associated with special suction boxes so that the belts, in effect,constitute a movable suction box top and the perforations in them arequite comparable with those normally formed in fixed suction box tops.The rubber belts of the prior art usually are dragged along by theFourdrinier screen, and while they may be effective to reduce, to alimited extent, the abrasive wear upon the screen they are necessarilyvery heavy and stiff, and they place an additional power demand upon thescreen. Also, they require special suction box tops having such aperforation pattern as to be usable only in combination with rubberbelts of a particular design.

In contrast with the prior art the present invention makes use of a belt52 woven from synthetic yarns and preferably woven in endless form toavoid the need for transverse joints. The belt 52 is thus a fabric comparable to the non-metallic fabric from which Fourdrinier screens havebeen made, but in most cases the belt fabric may be made of heavier orcoarser yarns and the weave may be more open. Such a coarse open fabricwould normally not be useful as a Fourdrinier screen because it wouldtend to pass too many fibers, it would mark the paper or other fibrousproduct being produced, and would also cause the formation to be souneven as to be unacceptable for almost any sort of fibrous product.However, such a coarse, relatively open fabric has been found to be anideal support for a Fourdrinier screen which may may be of suchconstruction as not to be practical for use alone in the conventionalmanner.

In the form of the invention shown in FIGURE 1, the supplementalscreen-like belt 52 is an idler belt whereby the power required to dragit across the suction boxes 40 must be derived from the Fourdrinierscreen 10. However, because of the light weight and flexibility of thebelt 52, the power demand is very much less than it has been for theheavy perforated rubber belts heretofore used. Beyond this, however, thesurface textures of the belt 52 and screen are such that they tend tomesh with one another whereby the belt 52 readily moves with the screen10. As diagrammatically shown in FIGURE 2, the Fourdrinier screen 10 ismade up of transversely extending yarns or wires 58 and longitudinallyextending yarns or Wires 60, and the fabric belt 52 is made up oftransversely extending yarns 62 and longitudinally extending yarns 64.While a plain weave is shown in each instance it will be understood thatany of the various weaves heretofore used for Fourdrinier screens, forexample, may be used for the screen 10 and belt 52 disclosed herein.Also, while it is customary in the manufacture of Fourdrinier screensfrom metallic wire to have the warps run lengthwise of the screen, withwelded or brazed joints to form an endless belt, it is preferred, whenFourdrinier screens are made from synthetic yarns to weave them endlessso as to avoid the need for a joint or seam. In the present inventionthe screen 10 may be metallic or non-metallic as desired, but forpurposes of illustration the screen 10 shown in FIGURE 2 is of theconfiguration assumed in an endless-woven structure. Thus, thetransversely extending wires or yarns 58 have the undulating shapecharacteristic of warps, while the longitudinally extending wires oryarns 60 have the straight shape characteristic of wefts.

Irrespective of the construction of or material used for the screen 10is it a particular feature of the present in-- vention that the fabricbelt 52 be non-metallic and it is preferred that it be woven in tubularform on the loom whereby the longitudinally extending yarns 64 are weftsand the transversely extending yarns 62 are warps. It IS believed thatmaximum benefits of the present invention are achieved when both thescreen 10 and belt 52 are non metallic endless-woven fabrics, and FIGURE2 is intended to illustrate the combination of these preferred fabrics.Thus, the transversely extending yarns 58 and 62 of both fabrics shownin FIGURE 2 have been illustrated as undulating above and below thewefts 60 and 64 in the manner which is characteristic of warp yarns in awoven fabric.

In all preferred forms of the present invention the supplemental belt52, at least, is Wovenin such a manner that the transversely extendingyarns are undulating and therefore form knuckles which make up thesurface of the fabric. These knuckles give the belt 52 a surface texturewhich tends to mesh with the Fourdrinier screen 10 whereby the belt 52will readily move in a longitudinal direction with the screen 10 whenthe papermaking machine is in operation. In the specifically preferredform shown in FIGURE 2 wherein the Fourdrinier screen 10 also has theundulating yarns extending transversely, the resistance to slipping inthe longitudinal direction in which the screen 10 and belt 52 move inuse is unusually good.

Beyond the fact that driving of the supplemental screenlike idler belt52 as shown in FIGURE 1 requires very little power from. the Fourdrinierscreen 10, the interpositioning of an idler belt 52 constructed inaccordance with the present invention between the Fourdrinier screen 10and the suction box tops brings about a very great reduction in thetotal amount of power which must be exerted through the Fourdrinierscreen 10. The relatively coarse woven structure of the belt 52 presentsmany fewer points of frictional contact with the suction box tops thanis presented by a Fourdrinier screen of ordinary construction. Thesepoints of contact are between the knuckles of the transversely extendingwarps 62 and the suction box tops. Consequently abrasive wear is on theknuckles and not on the longitudinally extending yarns 64 whereby thelongitudinal tensile strength of the belt 52 is not progressivelyreduced by such wear as would be the case if the knuckles were in thelongitudinal yarns. Full advantage of this characteristic of the beltsof the present invention may be realized by using suction box tops whichare highly resistant to abrasion and preferably are smoothly polished.For example, the suction box tops 42 may be made of stainless steel andthe upper surfaces thereof may be polished prior to installation in themachine. After the machine is placed in operation the movement of thebelt 52 across the polished surfaces of the suction box tops 42 mayfurther polish and smooth the surfaces, but grooving or galling of thesurfaces has not been observed, even after extremely long periods ofoperation. The coeificient of friction between the belt 52, which iswoven from synthetic yarns, and the smooth hard suction box tops 42 isextremely low with the result that the force required to pull the belt52, the Fourdrinier screen 10 and the fibrous stock 68 (see FIGURE 2)carried by the screen 10 across the suction boxes 40, with the latter innormal operation, is very much less than has been required in anycombination of which applicant is aware.

The customary practice in the past has been to use metallic Fourdrinierscreens which are dragged across the suction box tops in direct contacttherewith. Since the bronze or other alloys normally used in metallicFourdrinier screens have relatively low abrasion resistance and becauseof the almost inevitable presence of gritty or metallic particles in thepulp, the suction box tops have been made of wood or relatively softplastic materials which wear much more rapidly than the metal in thescreen. Steel suction box tops would be impractical for use withmetallic Fourdrinier screens not only because of the expected rapid wearupon the screens but also because the gritty particles in the pulp causegrooving of the metal box tops and the metallic particles in the pulpcause galling between the metal Wire and metal tops with consequentdestruction of the screen.

The wood or plastic suction box tops heretofore necessarily used withmetallic Fourdrinier screens require frequent resurfacing to removegrooves and other imperfections caused by wear and such resurfacingcauses frequent shut-down of the papermaking machine. They also offervery substantial frictional resistance to the dragging of the screenacross the suction boxes when the machine is in operation, and the powerrequired to overcome this resistance must be exerted upon that portionof the screen which extends forwardly from the suction boxes to thecouch, or driving, roll. As discussed above, the demand for longitudinaltensile strength to overcome this resistance alone has placed severelimitations upon the design of metallic Fourdrinier screens.

It is a feature of the present invention that hard metal suction boxtops may be used when a non-metallic Fourdrinier screen woven fromsynthetic materials, such as nylon and other materials discussedhereinbelow, is used, with or Without the non-metallic supplemental belt52, and it is a further feature of this invention that such metalsuction box tops may be used with a metallic Fourdrinier screen when thenon-metallic belt 52 is interposed between the screen and the suctionbox tops as shown in FIGURE 1. In all such cases the material in contactwith the suction box tops is the non-metallic material described hereinand the advantages of long service life for the last mentioned material,reduced power demand and substantially complete elimination ofresurfacing of suction box tops, are achieved. When the non-metallicbelt 52 is used as Shown in FIGURE 1 with either a metallic ornon-metallic screen 10 the further advantage of vastly reduced wear uponthe screen 10 and even greater reduction in power demand are achieved.

In the form of the invention shown in FIGURE 3, all of the majorelements of the papermaking machine already described in connection withFIGURE 1 are shown and are identified by the same reference charactersas used in FIGURE 1, whereby description of said elements need not berepeated at this point. In FIGURE 3, however, the supplementalscreen-like belt is differently arranged. Thus, the supplemental belt152 not only extends from a roll 54 over the suction boxes 40 but itcontinues beneath the Fourdrinier screen 10 around the couch roll 14 tothe return guide roll 16. At the return guide roll 16 the belt 152 isseparated from the Fourdrinier screen 10 and the edge sensing paddles 17may be arranged to engage the edges of belt 152. In such event thereturn guide roll 16 will guide both the belt 152 and screen 10 inresponse to the sensing of the belt 152. The belt 152 may be tensionedby movement of the roll 54 in some cases, or by a belt tensioning roll160 carried on an arm 162 secured to a shaft 164 for rotatableadjustment about the axis 166 of the shaft 164 as may be desired. Thebelt 152 then continues to the belt guide roll 54 to complete itsendless path. The screen 10 should be separately guided and to this endthe roll 18 may be a return guide roll with edge sensing paddles 19.

The modification of the invention illustrated in FIG- URE 3 affords allof the advantages obtained by use of the modification shown in FIGURE 1,and in addition affords the very great advantage of relieving theFourdrinier screen 10 from a substantial portion of the longitudinalstresses incident to the driving of the screen through its endless path.In this form of the invention the supplemental screen-like belt 152 isnot an idler, as in FIGURE 1, but rather serves to drive the Fourdrinierscreen 10 because it lies beneath the screen at the couch roll 14. Thus,the power required to drag the belt 152 and the Fourdrinier screen 10over the suction boxes 40 is exerted through the belt 152 instead ofthrough the screen 10.

Because the modification shown in FIGURE 3 relieves the Fourdrinierscreen 10 from the longitudinal stresses due to movement across thesuction boxes it will be apparent that the Fourdrinier screen 10 may beeven lighter in construction, if so desired, than it might need to befor use in the modification shown in FIGURE 1. Accordingly, thisparticular form of the invention affords the designer of the Fourdrinierscreen an even greater latitude than is afforded by the form shown inFIGURE 1.

FIGURE 4 illustrates a still further modification of the presentinvention. The principal elements of the papermaking machine illustratedin FIGURE 1 are also shown in FIGURE 4 and are indicated by the samereference numerals as are used in FIGURE 1 to avoid the necessity forrepetition of description of such elements. However,

in the modification shown in FIGURE 4 a supplemental belt 252 is shownwhich is positioned inside of and extends with the Fourdrinier screen 10through almost all of the path of the latter. Thus, the belt 252 isinterposed between the Fourdrinier screen 10 and substantially all ofthe elements of the papermaking machine over which the Fourdrinierscreen 10 would normally pass to protect the screen 10 from wear and torelieve it from almost all stresses.

In FIGURE 4 the supplemental belt 252 extends in face-to-face engagementwith and beneath the Fourdrinier screen 10 around the breast roll 12 andover the forming board 34, over the table rolls 36 and other dewateringdevices such as 38. The belt 252 continues beneath the screen 10 overthe suction boxes 40 and around the couch roll 14, to the return guideroll 16. At the return guide roll 16 the belt 252 may be guided awayfrom the Fourdrinier screen 10 to pass over a belt tensioning roll 260carried by an arm 262 secured to a shaft 264 for rotatable adjustmentabout the axis 266 of the shaft 264. From the belt tensioning roll thebelt 252 extends to the return roll 18 Where it rejoins the Fourdrinierscreen 10 for travel with the same through the endless path justdescribed. Separate guiding of the screen 10 must be provided. Forexample, an additional return guide roll (not shown) may be positionedin the independent portion of the path of the screen 10. Alternatively,separate guiding may be provided by making the tension roll 20 alsoserve as a guide roll, with edge sensing paddles 21 engaging the edgesof screen 10.

By proper adjustment of the respective tensioning rolls 258 and 20 thebelt 252 and screen 10 may be made to ride together smoothly with thebelt 252 assuming almost all of the stresses and Wear to which theFourdrinier screen 10 ordinarily would be subjected. From the standpointof tension alone, the designer of a Fourdrinier screen 10 for use in anembodiment such as that shown in FIGURE 4, is almost unlimited in hisability to make use of light and delicate fabrics including many whichcould never be used alone for Fourdrinier screens.

In FIG. 5 a supplemental belt 352 is arranged and guided in the samemanner as the belt 252 in FIG. 4, except that the belt 352 does notextend around the breast roll 12. As shown in FIG. 5 the belt 352 isseparated from the screen 10 at the return roll 18 and extends upwardlyto a special roll 336 which is positioned in place of one of the tablerolls 36. The belt 352 may be sop arately tensioned in the manner shownin FIG. 4 or, alternatively, the special roll 336 may be mounted forhorizontal adjustment. In this form of the invention the supplementalbelt 352 is not beneath the Fourdrinier screen 10 as the latter passesbeneath the slice 30, and over the forming board 34 and, if so desired,a selected number of the table rolls 36. Thus, the critical earlyformation of the sheet 68 occurs on the unbacked screen 10 and this maybe preferred in certain instances as will be discussed below.

While FIG. 2 has been identified above as an enlarged fragmentarysection taken along the line 22 of FIG. 1, it is equally characteristicof a similar section in FIGS.

3, 4 or 5. Also, it will be recognized that even at the enlarged scaleemployed for FIG. 2 the representation of the supplemental belt 52,screen 10, and layer of deposited paper fibers 58 is necessarilydiagrammatic. This is also true of the fragmentary plan view presentedin FIG. 6 which is enlarged to a lesser degree than FIG. 2. FIGS. 2 and6 are intended to convey, within the limits of practicality, typicalrelative proportions of the suction box holes 44, 46, the layer offibers 68 and the fabrics which comprise the belt 52 and Fourdrinierscreen 10. The proportions are based on one illustrative installationparticularly adapted for the manufacture of a corrugatingboard. In thisparticular installation the holes 44 and 46 in the suction box top 42are circular and they are approximately one-half inch in diameter. Thesupplemental belt 52 is woven from synthetic yarns and there aretwenty-four warp yarns 62 per inch and there are twenty weft yarns 64per inch. The Fourdrinier sceen is woven from synthetic yarns with sixtywarp yarns 58 per inch and forty weft yarns 60 per inch. Thus, sinceFIG. 2 is a section taken across the wefts and parallel with the warpsit will be observed that there are approximately ten weft yarns 64within the portion of the belt 52 which spans the diameter of a singlesuction box hole 44 or 46. Similarly, there are approximately twentyweft yarns 60 within the portion of the Fourdrinier screen 10 whichspans the diameter of a single suction box hole 44 or 46. A typicalsupplemental belt 52 woven from synthetic yarns to the countillustratively set forth above may have a tensile strength in themachine direction, that is in the direction of the wefts, of about. 815pounds per lineal inch. In contrast with this, a typical Fourdrinierscreen 10 woven from synthetic yarns to the count illustratively setforth above may have a tensile strength in the machine or weft directionof about 380 pounds per lineal inch. In another typical installationsuitable for the manufacture of fine paper or paper made from stockcontaining a substantial quantity of short'fibers or filling materialwhere high fines retention is desirable, the Fourdrinier screen 10 maybe woven from yarns of synthetic material to much higher counts. Forexample,a count of ninety warps per inch and ninety wefts per inch maybe used. A typical fabric woven to such a count from carefully selectedsynthetic materials and stabilized as will be discussed more fullybelow, may have a tensile strength in the machine or weft direction ofabout ninety pounds per lineal inch. With such a screen 10 thesupplemental belt 52 provided in accordance with the present inventionmay be the same strong, relatively coarse fabric described above inconnection with the manufacture of a corrugating board, or it may besomewhat finer if so desired. In any event, the supplemental belt 52 canbe substantially coarser in weave and, where desirable, it may have upto several times greater machine-direction tensile strength than thescreen 10.

In the form of the invention shown in FIG. 1, wherein the supplementalbelt 52 is an idler, the superior tensile strength of the belt 52 is notfully utilized, but the fact that the belt 52 may be relatively coarsein weave provides the great advantage, as pointed out above, of lowfriction movement across the suction box tops with resultant reductionin power demand upon the screen 10. However, the form of the inventionshown in FIG. 1 may be further modified in a well-known manner byproviding suitable means for driving the roll 56 at a peripheral speedmatching that of the screen 10 whereby to relieve the screen 10 ofadditional longitudinal stresses.

In the form of the invention shown in FIG. 3 wherein the supplementalbelt 152 extends across the suction boxes and around the couch roll 14,the great tensile strength of the belt 152 may be utilized inasmuch asit reinforces the screen 10 throughout the zone wherein the greatestlongitudinal stress ordinarily is exerted upon the screen.

In the form of the invention shown in FIG. 4 wherein the supplementalbelt 252 runs beneath the screen 10 around the breast roll 12, acrossall of the dewatering devices and table rolls, suction boxes and aroundthe couch roll, the maximum advantage of the great tensile strength ofthe supple-mental belt 252 and the independent tensioning of the belt252 and the screen 10 is realized. In this form of the invention thesupplemental belt 252 may be placed under sufficient tension to preventstock jump at the table rolls irrespective of the fineness andrelatively low tensile strength of the screen 10. In this embodiment ofthe invention the screen 10 needs only to be placed under sufficienttension by means of its individual tensioning roll 20 as to insure thatit will move with the supplemental belt 252 in a smooth and uniformmanner.

In the form of the invention shown in FIG. 5, almost all of theadvantages flowing from the superior tensile strength of thesupplemental belt 352 may be realized. As shown in FIG. 5, the screen 10travels independently of the belt 352 through a relatively short portionof its endless path, and this portion is in the zone wherein very littlemachine direction stress is placed upon the screen 10. By guiding thesupplemental belt 352 into engagement with the screen 10 at a positionwithin the table roll and dewatering section just ahead of the zone inwhich stock jump may present a problem, the screen 10 need not be placedunder any great amount of tension because the tension upon the belt 352may be relied uponto prevent stock jump in the critical areas. It willbe understood that while FIG. 5 shows the belt 352 brought intoengagement with the screen 10 after it has passed several table rolls36, the belt 352 may be brought beneath the screen at any point ahead ofor behind the particular point chosen for illustration. For example, thebelt 352 might be brought into engagement with the screen 10 at theposition occupied by the first table roll 36.

The problem of stock jump has been discussed above in so far as itsrelation to screen tension is concerned, but it will understood that,from a theoretical standpoint at least, the application of anyincreasing amount of longitudinal tension short of an infinite tensionwill not be completely effective to overcome the tendency of the screen10 to wrap each of the table rolls over which it passes. However, amajor cause of the tendency of the screen 10 to wrap a table roll isthat each table roll acts as a pump carrying water and air away from thezone beneath the Fourdrinier screen. The screen is therefore caused tofollow the table roll surface by the differential between theatmospheric pressure above the aqueous fibrous suspension carried by thescreen, and the subatmospheric pressure on the downwardly moving side ofthe table roll. Since this differential sharply increases with increasesin machine speed, it has been necessary to increase the screen tensionvery sharply or to make expensive structural alterations in a papermachine to accommodate it to higher speeds. In the forms of the presentinvention illustrated in FIGS. 4 and 5, the supplemental belts 252 and352 may be utilized to control the differential and thus permitoperation of a papermaking machine at greatly increased speeds withoutthe need for increased tension to prevent stock jump. Reference to FIGS.2 and 6 will reveal that the coarse open structure of the supplementalbelt 52 affords openings of large volume between the yarns. The drainagerate of a screen 10 relative to a belt 252 or 352 in FIGS. 4 or 5, maybe adjusted by relating the volume and the relative sizes of theopenings between the yarns of the two fabrics so that the water thatflows through the screen 10 as the fabrics pass over the table rolls 36will not fill the opening in the belt 252 or 352. Under these conditionsair may circulate freely in generally horizontal directions in andbetween the openings in the belt 252 or 352. This circulating air willmaintain the gaseous pressure on the downwardly running sides of thetable rolls at a considerably higher value than would be the case if thefabric in engagement with the table roll were tobe filled with water, asin the case in an ordinary installation involving a single Fourdinierscreen. Thus, for a particular papermaking machine with table rolls of agiven diameter, the supplemental belts 252 or 352 and the screen may beso designed as to establish the efficiency of the table rolls as pumpsat a level where stock jump is avoided and the drainage rate is optimumfor formation and water removal at almost any particular machine speedwhich may be desired.

In utilizing the present invention it must be taken into considerationthat the rate at which water will drain through a screen 10 of anyparticular construction is substantially greater when the screen 10 isin contact with any of the supplemental belts herein disclosed than itwould be through the screen 10 alone.

Reference to FIG. 2 will reveal that the knuckles in the warp yarns 62on the upper surface of the fabric belt 52 provide an enormous number ofseparate contact points with the lower surface of the screen. Each suchcontact point will serve to break the surface tension of the water inthe screen 10 with the result that the flow of water through the screenis constantly being initiated and promoted in the vicinity of eachcontact point. This phenomenon is similar to that observed in a canvascamping tent, the roof of which may be substantially impervious to waterexcept at any point where it may be touched on the inside. As a resultof this phenomenon it is possible to use a screen 10 woven very closelyof water repellent yarns or wires having openings between yarns or wiresso small that water would not flow therethrough without inducement. Withsuch fine-mesh screen 10 resting upon the supplemental belt provided inaccordance with the present invention, the flow of water through thescreen is induced throughout the area of contact with the belt ratherthan only at the table rolls, suction boxes or other dewatering devices.The advantages of using such finemesh screens 10 are manifold andinclude exceedingly high fines retention, early and rapid build-up of alowermost layer of fibers and other papermaking constituents upon thescreen, and extremely smooth and uniform surface on the screen side ofthe paper.

Because of the presence of the relatively coarse mesh supplemental beltsprovided by the present invention directly beneath the screen 10, shadowmarking might be expected. However, this is not the case even withexceedingly finely woven Fourdrinier screens so long as water is notforced by the table rolls, for example, to fiow through the screen atsuch a high rate as would be objectionable anyhow from the standpoint ofpoor formation throughout the paper sheet. It it believed that one ofthe factors which contribute to the absence of shadow marking in thepractice of the present invention, is the fact that the screen 10 andthe supplemental belts 52, 152, 252 or 352 are separate fabrics whichmore or less continuously move or shift relative to one another as theyare driven through their respective paths. For example, it has beenfound that the screen and the supplemental belt drift back and forthrelative to one another in directions transverse the path of travel fordistances sometimes as great as about two inches. For this reason it ispreferable, as shown in FIG. 6, to make the supplemental belt 52somewhat wider than the screen 10 so that the longitudinal edges of thescreen 10 will not overlap the edges of the supplemental belt. While thedrifting referred to is kept to a small amount by the automaticindividually acting return guide rolls described above, there inevitablywill be sufiicient drifting in transverse direction to cause thepatterns of the two fabrics to shift relative to one another. It alsohas been observed that the outer fabric, that is the screen 10, willcreep ahead of the lower fabric because of its tendency to run at aslightly higher average longitudinal speed. When it is considered thatthe diameter of the yarns and the spacing between the yarns in even thecoarsest fabric might be used as a supplemental belt in practicing thisinvention, are only a small fraction of an inch, it will be recognizedthat even the small amount of drifting or creep between the fabricswhich occurs in each circuit of the machine is sufficient tocontinuously change the flow patterns through the interstices of the twofabrics.

It has been pointed out above that any of the supplemental beltsemployed in accordance with the present invention are preferably made ofa synthetic woven material and several reasons for such preference havealready been stated. An additional reason for the use of such materialsrather than a woven metal screen, for example, is that by proper choiceof materials or combinations of materials utilized in the yarns fromwhich the belts of the present invention are woven, the fatigueresistance of the synthetic fabrics can far exceed the fatigueresistance of a metal screen of equivalent coarseness under theconditions encountered in a papermaking machine. It will be recognizedthat endless belts are repeatedly bent back and forth as they pass overthe driving rolls, guide rolls and the like, as well as when they passover the table rolls and suction boxes. Such repeated flexure of metalwire screens causes workhardening thereof which eventually leads tofracture. Furthermore, in a papermaking machine the Fourdrinier screeninherently is subjected to varying amounts of tension in the directionof movement thereof, the tension normally being the greatest in thatportion of the screen which extends from the last suction box to thecouch roll. As the screen passes around the couch roll the tension isprogressively reduced from this maximum to substantially the minimumlongitudinal tension which exists after the screen leaves the lowersurface of the couch roll and enters its return path. At high machinespeeds the cycling between high and low longitudinal tension is veryrapid and leads to fatigue failure in metal screens. Fabrics inaccordance with the present invention can be so constructed as towithstand a substantially greater number of flexural or tension cyclingsthan can be withstood by metal screens of similar coarseness under thetensile loading conditions which are encountered in a papermakingmachine.

All of the supplemental belts of the present invention substantiallyreduce, and some almost entirely eliminate, the ordinarily highlongitudinally stresses to which the Fourdrinier screen 10 is subjected.They also reduce at least some of the flexural stresses thereon, forexample, at the table rolls and at the suction boxes. Accordingly, thescreens 10 for use in the present invention may be designed with muchless than usual regard for the danger of fatigue failure. It is for thisreason that Fourdrinier screens woven from metal wire or combinations ofmetal and synthetic or glass fiber yarns, may be used with thesupplemental fabric belts of the present invention although, as statedabove, the full advantages of this invention are believed to be bestachieved by the use of synthetic fabrics for both the screen and belt.When synthetic screens 10 are used they may be woven from yarns selectedfrom the same groups of materials and yarn constructions discussed belowin connection with the supplemental belts.

The supplemental screen-like fabric belts 52, 152, 252 and 352 arepreferably woven from a synthetic material having high tensile strengthand great abrasion resistance whether wet or dry, and nylon has beenmentioned above as a suitable material having these characteristics insuch degree as to be particularly useful for the purposes of thisinvention. Nylon yarns in the form of monofilament, multifilament orstaple fiber yarns may be used as warp or weft, or both, and differentforms may be used as warp and weft respectively. There are othersynthetic fiber forming materials available at the present time whichhave characteristics such as to be adequate for use in this invention,and it is reasonable to expect I that new materials of similar orsuperior characteristics will be developed in the future. Some of theseother materials may be used alone to produce yarns of multifibers oryarns to form heat-settable compositions.

13 filament, monofilament or staple fiber types, or filaments or fibersmade of such materials may be blended with others or with nylonfilaments or fibers to produce multifilament or staple fiber yarnssuitable for use as warp or weft, or both, in the manufacture of fabricsfor this invention. No effort will be made herein to make a tie tailedclassification of specific characteristics of fabrics woven from suchmaterials or blends, or combinations thereof. However, nylon6, nylon6-6, nylon 6-10, nylon 11, Dacron, polyethylene and glass are presentlyavailable and have been found to be particularly suitable. Dacron orglass may be formed into monofilaments or independent fine filaments foruse in multifilament yarns, and individually encased in a suitable typeof nylon, if

so desired, whereby the composite filament will exhibit desirablesurface characteristics of nylon and yet have such desirable additionalcharacteristics as the encased, or core, material may afford. Any of thematerials named above, or composites or blends thereof, may be utilizedas multifilament yarns or staple fiber yarns of cabled or pliedconstruction, as may be desired, and any particular fabric may haveyarns made of the same or different material or of the same or differentconstruction in the warp or weft.

Fabrics for use as the supplemental belts 52, 152, 252 or 352 disclosedherein, are preferably woven endless. Among the advantages thus achievedis avoidance of the need for splicing or otherwise joining the ends toform endless belts. However, in many papermaking machines it may beinconvenient or time-consuming to install an endless belt in any one ormore of the positions illustrated herein, and particularly when suchmachines are in production of some product in which marking of theproduct is not objectionable it may be economically prefer-able toprovide the belts with some form of fastening means by which the endsmay be joined after installation. For such instances, the belts may beWoven endless so that the wefts run longitudinally and they may be cuttransversely. Also, they may be Woven as flat fabrics with the warpsrunning longitudinally. In either event, the ends may be joined, afterinstallation, by sewing, or lacing, or by adhesives, or any combinationthereof, or the ends of the belts may be provided with loops or metalclips adapted to receive a pintle to form a hinged joint as iswell-known in the art.

The fabrics for use as supplemental belts 52, 152, 252 or 352 arepreferably stabilized to prevent shoving of the yarns and to minimizedimensional changes under the varying tensile stresses and moistureconditions to which they are subjected in use and during start-ups andshutdowns of the machine. The fabrics may be stabilized by heat-settingof some or all of the fibers therein with or Without the application ofchemicals which react with or coat, .or both, some or all of the fibersor yarns to stiffen or otherwise to change the characteristics of thefibers or yarns, or the surfaces thereof. The applied chemicals maythemselves be heat-settable or curable, or they may be of such a natureas to react with some or all of the It is preferred to stabilize thefabrics while in endless form whereby they may be brought to ormaintained in a specific yarn count, both warp and weft, which is bestcalculated to promote stability, and stabilized at that count. Forexample, a fabric having at least some yarns which consist at least inpart of nylon may be stabilized by heatsetting of the nylon,and'stability may be enhanced by applying an aldehyde resin to thefabric and heating the fabric, while held to desired yarn count, to cureand heatset the resin-coated nylon. The endless fabric which is thusstabilized may have been woven endless or may have been woven flat, andjoined to form an endless belt. After stabilization they may beinstalled and used in endless form or they may be cut in the crossmachine direction for ease of installation and joined, as describedabove, after they have been threaded upon the machine.

The service life of any of the fabrics used as supplemental belts asdisclosed herein, will be enhanced if the fabric is stabilized in such amanner that the transversely extending yarns undulate above and belowthe longitudinally extending yarns to protect the latter from abrasivewear. Thus, when the fabric is manipulated to bring it to desired countor to hold it in desired count care may be taken to assure that thelengthwise-extending yarns are substantially straight and the cross-wiseextending yarns undulate above and below the crossing points. The fabricis then set with the yarns so disposed. As indicated above, this resultis most readily achieved when an endless woven fabric is used.

What I claim is:

1. For use in a paper-making machine and the like having an endlessforming screen traveling through an endless path to receive an aqueoussuspension of fibers from which water drains through said screen toleave a layer of fibers on the outer surface of said screen, and havingone or more dewaterin-g devices positioned along a portion of saidendless path to promote the flow of water through said screen, anendless supplemental belt made of screen-like fabric substantially theentire area of which is woven exclusively from synthetic fiber-formingmaterial characterized by having whether wet or dry great tensilestrength great resistance to abrasion and great resistance to damage dueto flexing, said belt being arranged on said papermaking machine to movein an endless path inside the endless path of said forming screen, theendless paths of said forming screen and said belt substantiallycoinciding in a portion of the endless path of said forming screen inwhich said forming screen is advanced over at least one of saiddewatering devices whereby in said portion of said path said belt isinterposed between said forming screen and said dewatering devices withthe outer surface of said belt in face-to-face contact with the innersurface of said forming screen and the inner surface of said belt incontact with said dewatering devices, the fabric from which said belt isformed having the weft yarns extending longitudinally and the warp yarnsextending transversely of the path of movement of said belt, and thefabric of said belt being stabilized with the transversely extendingwarp yarns set in undulating form to provide knuckles extending aboveand below the longitudinally extending Weft yarns to protect said Weftyarns from abrasive wear and to mesh with the inner surface of saidforming screen to provide improved longitudinal driving engagementbetween those portions of said belt and said forming screen which are inface-to-face contact.

2. An endless supplemental belt in accordance with claim 1 for use in apapermaking machine and the like having a woven forming screen ofrelatively fine mesh, the fabric of said belt being substantiallycoarser in mesh than said forming screen.

References Cited by the Examiner UNITED STATES PATENTS 635,266 10/-1899Marshall 162-349 1,514,011 11/1'924 Pope 162-349 1,880,686 10/4932 Berry162349 2,903,021 9/1959 Holden 162-348 FOREIGN PATENTS 762,894 112/ 1956Great Britain.

Pye Pulp and Paper Magazine of Canada: pages 124-- 136.

DONALL H. SYLVEST-ER, Primary Examiner. RICHARD D. NEVIUS, Examiner.

1. FOR USE IN A PAPERMAKING MACHINE AND THE LIKE HAVING AN ENDLESSFORMING SCREEN TRAVELING THROUGH AN ENDLESS PATH TO RECEIVE AN AQUEOUSSUSPENSION OF FIBERS FROM WHICH WATER DRAINS THROUGH SAID SCREEN TOLEAVE A LAYER OF FIBERS ON THE OUTER SURFACE OF SAID SCREEN, AND HAVINGONE OR MORE DEWATERING DEVICES POSITIONED ALONG A PORTION OF SAIDENDLESS PATH TO PROMOTE THE FLOW OF WATER THROUGH SAID SCREEN, ANENDLESS SUPPLEMENTAL BELT MADE OF SCREEN-LIKE FABRIC SUBSTANTIALLY THEENTIRE AREA OF WHICH IS WOVEN EXCLUSIVELY FROM SYNTHETIC FIBER-FORMINGMATERIAL CHARACTERIZED BY HAVING WHETHER WET OR DRY GREAT TENSILESTRENGTH GREAT RESISTANCE TO ABRASION AND GREAT RESISTANCE TO DAMAGE DUETO FLEXING, SAID BELT BEING ARRANGED ON SAID PAPERMAKING MACHINE TO MOVEIN AN ENDLESS PATH INSIDE THE ENDLESS PATH OF SAID FORMING SCREEN, THEENDLESS PATHS OF SAID FORMING SCREEN AND SAID BELT SUBSTANTIALLYCOINCIDING IN A PORTION OF THE ENDLESS PATH OF SAID FORMING SCREEN INWHICH SAID FORMING SCREEN IS ADVANCED OVER AT LEAST ONE OF SAIDDEWATERING DEVICES WHEREBY IN SAID PORTION OF SAID PATH SAID BELT ISINTERPOSED BETWEEN SAID FORMING SCREEN AND SAID DEWATERING DEVICES WITHTHE OUTER SURFACE OF SAID BELT IN FACE-TO-FACE CONTACT WITH THE INNERSURFACE OF SAID FORMING SCREEN AND THE INNER SURFACE OF SAID BELT INCONTACT WITH SAID DEWATERING DEVICES, THE FABRIC FROM WHICH SAID BELT ISFORMED HAVING THE WEFT YARNS EXTENDING LONGITUDINALLY AND THE WARP YARNSEXTENDING TRANSVERSELY OF THE PATH OF MOVEMENT OF SAID BELT, AND THEFABRIC OF SAID BELT BEING STABILIZED WITH THE TRANSVERSELY EXTENDINGWARP YARNS SET IN UNDULATING FORM TO PROVIDE KNUCKLES EXTENDING ABOVEAND BELOW THE LONGITUDINALLY EXTENDING WEFT YARNS TO PROTECT SAID WEFTYARNS FROM ABRASIVE WEAR AND TO MESH WITH THE INNER SURFACE OF SAIDFORMING SCREEN TO PROVIDE IMPROVED LONGITUDINAL DRIVING ENGAGEMENTBETWEEN THOSE PORTIONS OF SAID BELT AND SAID FORMING SCREEN WHICH ARE INFACE-TO-FACE CONTACT.